The present invention relates to signature stackers and more particularly to a novel stacker for forming either compensated or non-compensated bundles of a predetermined bundle size wherein the otherwise conventional means employed in present day stackers which serve to momentarily hold a portion of the signature stream in a stationary position is eliminated through the use of a novel swingable intercept assembly driven into rotation by non-linear drive means.
Stackers are typically used in the graphic arts industry wherein it is desired to form bundles of signatures such as, for example, magazines, newspapers and the like, wherein each bundle is comprised of a predetermined number of signatures. Signatures are typically delivered to the stacker in a continuous stream and are arranged in overlapping fashion. The delivery rate of signatures such as, for example, newspapers delivered from the press room, is typically in excess of 70,000 signatures per hour. It is therefore necessary to provide a stacker which is capable of separating the continuous stream into accurate size bundles and wherein stacking is performed at speeds sufficient to eliminate the need for slowing down the flow rate of signatures from the presses.
Conventional stackers are typically comprised of an infeed conveyor section which receives the signatures and which, in turn, is provided with means for counting the signatures as they pass therethrough. Some means must then be provided for intercepting the stream of signatures at a location intermediate the infeed and outfeed conveyors, at which latter location the signatures are neatly stacked into a bundle. One conventional type of intercept means is comprised of a plurality of buckets arranged at spaced intervals along a pair of closed loop chains driven so that while one bucket receives signatures from the incoming stream, at least one other bucket is locked into a non-intercept position in readiness for moving into the signature stream when the bundle on the moving bucket is completed.
The bucket receiving signatures is moved in a downward direction and continues to accumulate signatures until the predetermined bundle size is achieved, at which time the aforesaid counter means provides a trigger signal for unlatching the latched bucket thereby moving the unlatched bucket into the signature stream to begin a new bundle. Stackers of this type have been found to limit maximum bundle size for the reasons set forth, for example, in U.S. Pat. No. 3,479,932. In order to overcome the disadvantageous feature of limiting maximum bundle size a technique is described in the aforementioned U.S. Patent wherein two separate and independent sets of buckets are arranged on separate closed loop chain pairs and are independently driven to permit independent relative motion between the two sets of buckets arranged at intervals along their associated chain pairs. This technique, however, provides a quite complicated and expensive stacker structure.
Still another technique utilized in conventional stackers employs holding means provided in the in-feed conveyor section, which functions to hold or "clamp" the signature stream passing therethrough so as to introduce a gap in the signature stream for a time interval of a duration sufficient to permit the reciprocating stacker assembly to deliver the completed bundle to a bucket at the outfeed conveyor location and to return to its uppermost position in readiness for receiving signatures to form the next bundle. This technique has been found to be disadvantageous due to the fact that signatures (especially when still wet) have been found to curl or fold over as a result of the abrupt clamping operation so as to damage the clamped signatures, as well as the signatures immediately following the clamped signatures and to effect the neatness of the bundles being formed, as well as creating a potential jam condition.